IF a SA-β-galactosidase-activated lysosomal delivery conjugate — consisting of a thermostable microbial melanoidin/AGE-hydrolase (candidate: Bacillus or Pseudonocardia sp. extradiol dioxygenase/Maillard-product hydrolase, hereafter MHase-Gal) encapsulated within an acetylated-galactose-caged, lysosome-targeted nanocarrier, administered intraperitoneally at 3–10 mg/kg biweekly — is administered to aged (20–22 month) male and female C57BL/6J mice with confirmed high whole-body lipofuscin burden (quantified by ex vivo autofluorescence spectroscopy),

THEN a ≥30% reduction in lysosomal lipofuscin autofluorescence in hepatocytes and hippocampal neurons, restoration of lysosomal cathepsin B/D flux (≥1.5-fold increase vs. vehicle), suppression of SASP cytokine panel (IL-6, IL-1β, MMP-3, ≥40% reduction in serum), and a statistically significant extension of median remaining lifespan (≥10% vs. age-matched vehicle controls, log-rank p < 0.05) will be observed,

BECAUSE the following causal chain operates:

1. Lipofuscin, composed of covalently cross-linked oxidized proteins and oxidized lipids including bisretinoids and advanced glycation end-product (AGE)-modified proteins, is physically undegradable by endogenous mammalian lysosomal hydrolases, causing progressive lysosomal compartment enlargement and dysfunction in post-mitotic and senescent cells (Lipofuscin is a covalently cross-linked, autofluorescent aggregate refractory to lysosomal degradation)[https://doi.org/10.1016/j.redox.2017.01.017].

2. Lipofuscin accumulation in aging post-mitotic cells (neurons, microglia) causes lysosomal storage overload that directly impairs autophagy flux, creating a feedforward loop of aggregate accumulation and cellular senescence (Lipofuscin granules steadily accumulate in aging microglia, directly burdening lysosomal clearance function)[https://doi.org/10.1038/nn.4325].

3. Senescent cells with high lipofuscin burden exhibit markedly elevated SA-β-galactosidase (SA-β-gal, encoded by GLB1) activity within their enlarged lysosomes — the same compartment where lipofuscin resides — providing a molecular activation gate precisely co-localized with the target substrate [SPECULATIVE: selectivity of SA-β-gal upregulation correlating with lipofuscin mass rather than merely time-in-senescence has not been formally demonstrated but is implied by the lysosomal hypertrophy mechanism described in the evidence set].

4. The acetylated galactose cage of MHase-Gal renders the enzyme inactive in transit and in non-senescent cells; upon endocytosis into lipofuscin-high lysosomes, abundant SA-β-gal cleaves the galactose moiety, releasing and activating the enzyme in direct proximity to lipofuscin granules (SA-β-gal-mediated cleavage of galactose conjugates in senescent-cell lysosomes has been demonstrated for navitoclax, establishing mechanistic precedent for lysosomal prodrug/pro-enzyme activation as described by González-Gualda et al. 2020, referenced in the evidence set ...

SENS category: LysoSENS

Key references: • doi.org/10.1016/j.redox.2017.01.017]. • doi.org/10.1038/nn.4325]. • doi.org/10.1002/pmic.201300406]. • doi.org/10.1159/000490908]. • doi.org/10.1016/j.redox.2017.01.017],